Process for the manufacture of diesel range hydrocarbons

ABSTRACT

The invention relates to a process for the manufacture of diesel range hydrocarbons wherein a feed is hydrotreated in a hydrotreating step and isomerised in an isomerisation step, and a feed comprising fresh feed containing more than 5 wt % of free fatty acids and at least one diluting agent is hydrotreated at a reaction temperature of 200-400° C., in a hydrotreating reactor in the presence of catalyst, and the ratio of the diluting agent/fresh feed is 5-30:1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of copending application Ser. No.13/107,146, filed on May 13, 2011. application Ser. No. 13/107,146 is aDivisional of copending application Ser. No. 11/477,922 filed on Jun.30, 2006, now U.S. Pat. No. 8,022,258, which claims the benefit of U.S.Provisional Application No. 60/695,853 filed on Jul. 5, 2005. The entirecontents of all of the above applications is hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to an improved process for the manufacture ofhydrocarbons, particularly diesel range hydrocarbons from bio oils andfats, wherein the formation of higher molecular weight compounds isreduced. The invention also relates to processing of feedstockcontaining free fatty acids, using a high product recycle/freshoil-ratio at reduced reaction temperatures.

BACKGROUND OF THE INVENTION

Environmental interests and an increasing demand for diesel fuel,especially in Europe, encourage fuel producers to employ moreintensively available renewable sources. In the manufacture of dieselfuels based on biological raw materials, the main interest hasconcentrated on vegetable oils and animal fats comprising triglyceridesof fatty acids. Long, straight and mostly saturated hydrocarbon chainsof fatty acids correspond chemically to the hydrocarbons present indiesel fuels. However, neat vegetable oils display inferior properties,particularly extreme viscosity and poor stability and therefore theiruse in transportation fuels is limited.

Conventional approaches for converting vegetable oils or other fattyacid derivatives into liquid fuels comprise transesterification,catalytic hydrotreatment, hydrocracking, catalytic cracking withouthydrogen and thermal cracking among others. Typically triglycerides,forming the main component in vegetable oils, are converted into thecorresponding esters by the transesterification reaction with an alcoholin the presence of catalysts. The obtained product is fatty acid alkylester, most commonly fatty acid methyl ester (FAME). Poorlow-temperature properties of FAME however limit its wider use inregions with colder climatic conditions.

Said properties are the result of the straight chain nature of the FAMEmolecule and thus double bonds are needed in order to create evenbearable cold flow properties. Carbon-carbon double bonds and estergroups however decrease the stability of fatty acid esters, which is amajor disadvantage of transesterification technology. Further, Schmidt,K., Gerpen J. V.: SAE paper 961086 teaches that the presence of oxygenin esters results in undesirable higher emissions of NO_(x), incomparison to conventional diesel fuels.

Undesired oxygen may be removed from fatty acids or their esters bydeoxygenation reactions. The deoxygenation of bio oils and fats, whichare oils and fats based on biological material, to produce hydrocarbonssuitable as diesel fuel products, may be carried out by catalytichydroprocessing, such as hydrocracking, but also more controlledhydrotreating conditions may be utilized.

During hydrotreating, particularly hydrodeoxygenation oxygen containinggroups are reacted with hydrogen and removed through formation of waterand therefore this reaction requires rather high amounts of hydrogen.Due to the highly exothermic nature of these reactions, the control ofreaction heat is extremely important. Impure plant oil/fat or animalfat/oil, high reaction temperatures, insufficient control of reactiontemperature or low hydrogen availability in the feed stream may causeunwanted side reactions, such as cracking, polymerisation, ketonisation,cyclisation and aromatisation, and coking of the catalyst. These sidereactions also decrease the yield and the properties of diesel fractionobtained.

Unsaturated feeds and free fatty acids in bio oils and fats may alsopromote the formation of heavy molecular weight compounds, which maycause plugging of the preheating section and decrease catalyst activityand life.

The fatty acid composition, size and saturation degree of the fatty acidmay vary considerably in feedstock of different origin. The meltingpoint of bio oil or fat is mainly a consequence of saturation degree.Fats are more saturated than liquid oils and in this respect need lesshydrogen for hydrogenation of double bonds. Double bonds in a fatty acidchain also promote different kinds of side reactions, such asoligomerisation/polymerization, cyclisation/aromatisation and crackingreactions, which deactivate catalyst, increase hydrogen consumption andreduce diesel yield.

Plant oils/fats and animal oils/fat may contain typically 0-30% of freefatty acids, which are formed during enzymatic hydrolysis oftriglycerides especially when oil seeds are kept in humid atmosphere.Free fatty acids can be also formed during purification of bio oils andfats, especially during caustic wash i.e. alkali catalyzed hydrolysis.The amount of free fatty acids present in plant/vegetable oils istypically 1-5 wt % and in animal fat 10-25 wt-%. Free fatty acids arecorrosive in their nature, they can attack against materials of unit orcatalyst and can promote some side reactions. Free fatty acids reactvery efficiently with metal impurities producing metal carboxylates,which promote side reaction chemistry.

Fatty acids may also promote the formation of heavy compounds. Theboiling range of these heavy compounds is different from the range ofdiesel fuel and may shorten the life of isomerisation catalyst. Due tothe free fatty acids contained in bio oils and fats, the formation ofheavy molecular weight compounds are significantly increased compared totriglyceridic bio feeds, which have only low amount of free fatty acids(<1%).

Biological raw materials often contain metal compounds, organicnitrogen, sulphur and phosphorus compounds, which are known catalystinhibitors and poisons inevitably reducing the service life of thecatalyst and necessitating more frequent catalyst regeneration orchange. Metals in bio oils/fats inevitably build up on catalyst surfaceand change the activity and selectivity of the catalyst. Metals canpromote some side reactions, but blocking of catalyst active sitestypically decreases the activity and thus metal impurities such as Na,Ca, and Mg compounds should be removed as efficiently as possible.

Hydrolysis of triglycerides produces also diglycerides andmonoglycerides, which are partially hydrolyzed products. Diglyceridesand monoglycerides are surface-active compounds, which can formemulsions and make liquid/liquid separations of water and oil moredifficult. Bio oils and fats can also contain other glyceride-likesurface-active impurities like phospholipids (for example lecithin),which have phosphorus in their structures. Phospholipids are gum likematerials, which can be harmful for catalysts. Natural oils and fatsalso contain other types of components, such as waxes, sterols,tocopherols and carotenoids, some metals and organic sulphur compoundsas well as organic nitrogen compounds. These compounds can be harmfulfor catalysts or pose other problems in processing.

U.S. Pat. No. 4,992,605 and U.S. Pat. No. 5,705,722 describe processesfor the production of diesel fuel additives by conversion of bio oilsinto saturated hydrocarbons under hydroprocessing conditions with CoMoand NiMo catalysts. The process operates at high temperatures of350-450° C. and produces n-paraffins and other hydrocarbons. The producthas a high cetane number but poor cold properties (melting point >20°C.), which limits the amount of product that can be blended inconventional diesel fuels in summer time and prevent its use duringwinter time. The formation of heavy compounds with a boiling point above343° C. was observed, especially when a fatty acid fraction was used asa feed. A reaction temperature with a lower limit of 350° C. wasconcluded as a requirement for trouble-free operation.

A two-step process is disclosed in FI 100248, for producing middledistillates from vegetable oil by hydrogenating fatty acids ortriglycerides of vegetable oil origin using commercial sulphur removalcatalysts, such as NiMo and CoMo, to give n-paraffins, followed byisomerising said n-paraffins using metal containing molecular sieves orzeolites to obtain branched-chain paraffins. The hydrotreating wascarried out at rather high reaction temperatures of 330-450° C.,preferably 390° C. Hydrogenating fatty acids at those high temperaturesleads to shortened catalyst life resulting from coking and formation ofside products.

EP 1 396 531 describes a process containing at least two steps, thefirst one being a hydrodeoxygenation step and the second one being ahydroisomerisation step utilizing counter-current flow principle, andusing biological raw material containing fatty acids and/or fatty acidesters as the feedstock. The process comprises an optional strippingstep.

Deoxygenation of plant oils/fats and animal fats with hydrogen use alarge amount of hydrogen and at the same time releases significantamount of heat. Heat is produced from deoxygenation reactions and fromdouble bond hydrogenation. Different feedstocks produce significantlydifferent amounts of reaction heat. The variation of reaction heatproduced is mainly dependent on double bond hydrogenation. The averageamount of double bonds per triglyceride molecule can vary from about 1.5to more than 5 depending on the source of bio oil or fat.

FR 2,607,803 describes a process for hydrocracking of vegetable oils ortheir fatty acid derivatives under pressure to give hydrocarbons and tosome extent acid. The catalyst contains a metal dispersed on a support.A high temperature of 370° C. did not result complete oxygen removal orhigh selectivity of n-paraffins. The product mixture formed, containedalso some intermediate fatty acid compounds.

Formation of water during hydrotreatment results from the deoxygenationof triglyceride oxygen by the means of hydrogen (hydrodeoxygenation).Deoxygenation under hydrodeoxygenation conditions is to some extentaccompanied by a decarboxylation reaction pathway and a decarbonylationreaction pathway. Deoxygenation of fatty acid derivatives bydecarboxylation and/or decarbonylation reactions forms carbon oxides(CO₂ and CO) and aliphatic hydrocarbon chains with one carbon atom lessthan in the original fatty acid molecule. Decarb-reactions mean heredecarboxylation and/or decarbonylation reactions.

The feasibility of decarboxylation varies greatly with the type ofcarboxylic acid or derivative thereof used as the starting material.Alpha-hydroxy, alpha-carbonyl and dicarboxylic acids are activated formsand thus they are more easily deoxygenated by decarb-reactions.Saturated aliphatic acids are not activated this way and generally aredifficult to deoxygenate through decarb-reactions.

Decarboxylation of carboxylic acids to hydrocarbons by contactingcarboxylic acids with heterogeneous catalysts was suggested by Maier, W.F. et al: Chemische Berichte (1982), 115(2), 808-12. Maier et al testedNi/Al₂O₃ and Pd/SiO₂ catalysts for decarboxylation of several carboxylicacids. During the reaction the vapors of the reactant were passedthrough a catalytic bed together with hydrogen. Hexane represented themain product of the decarboxylation of the tested compound heptanoicacid. When nitrogen was used instead of hydrogen no decarboxylation wasobserved.

U.S. Pat. No. 4,554,397 discloses a process for the manufacture oflinear olefins from saturated fatty acids or esters, suggesting acatalytic system consisting of nickel and at least one metal selectedfrom the group consisting of lead, tin and germanium. With othercatalysts, such as Pd/C, low catalytic activity and cracking tosaturated hydrocarbons, or formation of ketones when Raney-Ni was used,were observed.

OBJECT OF THE INVENTION

An object of the invention is an improved process for the manufacture ofdiesel range hydrocarbons from bio oils and fats, with high selectivity,essentially without side reactions and with high diesel yield.

A further object of the invention is an improved process for themanufacture of diesel range hydrocarbons from bio oils and fats, whereinthe extent of high molecular weight compounds formed duringhydrotreating is decreased and the stability of the catalyst isincreased.

A still further object of the invention is an improved process for themanufacture of diesel range hydrocarbons from bio oils and fats, whereinthe hydrotreatment of triglyceride feedstock containing free fatty acidsis carried out using dilution of fresh feed and reduced reactiontemperature.

A still further object of the invention is an improved process for themanufacture of diesel range hydrocarbons from bio oils and fats, whichprocess produces high quality diesel component with high yield.

Characteristic features of the process according to the invention areprovided in the claims.

DEFINITIONS

Here hydroprocessing is understood as catalytic processing of organicmaterial by all means of molecular hydrogen.

Here hydrotreatment is understood as a catalytic process, which removesoxygen from organic oxygen compounds as water (hydrodeoxygenation, HDO),sulphur from organic sulphur compounds as dihydrogen sulphide (H₂S)(hydrodesulphurisation, HDS), nitrogen from organic nitrogen compoundsas ammonia (NH₃) (hydrodenitrogenation, HDN) and halogens, for examplechlorine from organic chloride compounds as hydrochloric acid (HCl)(hydrodechlorination, HDCl), typically under the influence of sulphidedNiMo or sulphided CoMo catalysts.

Here deoxygenation is understood to mean removal of oxygen from organicmolecules, such as fatty acid derivatives, alcohols, ketones, aldehydesor ethers by any means previously described.

Here hydrodeoxygenation (HDO) of triglycerides or other fatty acidderivatives or fatty acids is understood to mean the removal of carboxyloxygen as water by the means of molecular hydrogen under the influenceof catalyst.

Here decarboxylation and/or decarbonylation of triglycerides or otherfatty acid derivatives or fatty acids is understood to mean removal ofcarboxyl oxygen as CO₂ (decarboxylation) or as CO (decarbonylation) withor without the influence of molecular hydrogen. Decarboxylation anddecarbonylation reactions either together or alone are referred to asdecarb-reactions.

Here hydrocracking is understood as catalytic decomposition of organichydrocarbon materials using molecular hydrogen at high pressures.

Here hydrogenation means saturation of carbon-carbon double bonds bymeans of molecular hydrogen under the influence of a catalyst.

Here n-paraffins mean normal alkanes or linear alkanes that do notcontain side chains.

Here isoparaffins mean alkanes having one or more C₁-C₉, typically C₁-C₂alkyl side chains, typically mono-, di-, tri- or tetramethylalkanes.

The feed (total feed) to the hydrotreating unit is here understood tocomprise fresh feed and at least one dilution agent.

SUMMARY OF THE INVENTION

The present invention relates to an improved process for the manufactureof hydrocarbons from renewable sources, such as plant oils/fats andanimal oils/fats, comprising a hydrotreating step and an isomerisationstep. Particularly the invention relates to the transformation of thestarting materials comprising triglycerides, fatty acids and derivativesof fatty acids or combinations of thereof, into n-paraffins with reducedformation of high molecular weight hydrocarbons using dilution of freshfeed and reduced reaction temperature in the hydrotreating step andconverting the obtained n-paraffins into diesel range branched alkanesusing isomerisation, with high diesel yield. The hydrotreating step iscarried out contacting the feed comprising fresh feed and at least onediluting agent with a hydrotreatment catalyst under hydrotreatmentconditions. Then the obtained product is isomerised with anisomerisation catalyst under isomerisation conditions. The hydrocarbonoil formed via this process is a high quality diesel component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the operation of the hydrotreatment process.

FIG. 2 shows the increase of formation of high molecular weighthydrocarbons when 10 wt-% free fatty acids was fed along with purifiedrapeseed oil triglycerides without product recycle.

FIG. 3 shows the effect of product recycle on preventing the formationof unwanted higher molecular weight by-product.

FIG. 4 shows reaction temperature profile over catalyst bed andperformance of crude rapeseed oil.

FIG. 5 shows performance of crude animal fat.

FIG. 6 shows the conversion of rapeseed oil triglycerides ton-paraffins.

FIG. 7 shows the stability of catalyst as stabile operation wasmaintained and the formation of heavies was steady over the whole testrun of over 9 months.

FIG. 8 shows that the bromine indexes increased during run even iftemperature compensation of catalyst was used.

DETAILED DESCRIPTION OF THE INVENTION

It was surprisingly found that dilution of fresh feed in thehydrotreatment step, in combination with decreased reaction temperaturereduces the undesired side reactions and improves reaction selectivity,particularly when a starting material containing free fatty acids isused. The diluting agent can be a hydrocarbon of biological originand/or non-biological origin. The dilution agent can also be recycledproduct from the process (product recycle). The diluting agent/freshfeed-ratio is 5-30:1, preferably 10-30:1 and most preferably 12-25:1.

A preferable embodiment of the invention and of the hydrotreatment stepis illustrated in FIG. 1, wherein a hydrotreatment process configurationis provided, comprising one or more catalyst beds in series,hydrotreated product recycle introduction on the top of the firstcatalyst bed and fresh feed, quench liquid and hydrogen introduction ontop of each catalyst beds. This results in improved control of thereaction temperature in the catalyst beds and hence diminishes undesiredside reactions.

In FIG. 1 the hydrotreatment reactor 100 comprises two catalyst beds 10and 20. Fresh feed 11 is introduced as streams 12 and 13 on the catalystbeds 10 and 20, respectively, and hydrogen as stream 22 and 23 on thecatalyst beds 10 and 20, respectively. The fresh feed stream 12 is firstmixed with the hydrotreated product recycle stream 41 and quench liquidstream 43 and the resulting mixture 31, diluted in the fresh feedconcentration, is then introduced on the catalyst bed 10. In order toobtain a required sulphur concentration in the feed stream 31, requiredamount of sulphur make up is added to the fresh feed stream 11 viastream 15. As mixture 31 passes through the catalyst bed 10 with thehydrogen stream 22, fatty acids and fatty acid derivatives of the freshfeed stream 12 are converted to the corresponding reaction products. Atwo-phase stream 32 is withdrawn from the bottom of the catalyst bed 10and is mixed with the fresh feed stream 13, quench liquid stream 44 andthe hydrogen stream 23. The formed vapor-liquid mixture 33, diluted inthe fresh feed concentration, is then introduced on the catalyst bed 20at reduced temperature due to cooling effect of the hydrogen, quenchliquid and fresh feed, passed through the catalyst bed 20 and finallywithdrawn from the catalyst bed as a product stream 34. The stream 34 isseparated in to a vapor stream 35 and liquid stream 36 in the hightemperature separator 101. Vapor stream 35 is rich in hydrogen and isdirected to further treatment. Part of the liquid stream 36 is returnedto the reactor 100 as recycle stream 40, which is further divided todilution stream 41 and total quench liquid stream 42. The quench liquidstream 42 is cooled in the heat exchanger 102 to provide adequatecooling effect on the top of the catalyst beds 10 and 20. Hydrotreatedproduct stream 51 is directed from the hydrotreatment step to furtherprocessing.

The catalyst beds 10 and 20 may be located in the same pressure vesselor in separate pressure vessels. In the embodiment where the catalystbeds are in the same pressure vessels the hydrogen streams 22 and 23 mayalternatively be introduced on the catalyst bed 10 and then be passedthrough the catalyst beds 10 and 20. In the embodiment where thecatalyst beds are in separate pressure vessels, the catalyst beds mayoperate in parallel mode with separate dilution streams, hydrogenstreams and quench liquid streams. The number of catalyst beds may beone or two or more than two.

The sulphur make up to the hydrotreatment step may be introduced withthe fresh feed stream 11. Alternatively, required amount of sulphur maybe fed with the hydrogen streams 22 and 23 as gaseous sulphur compoundsuch as hydrogen sulphide.

Hydrogen is fed to the hydrotreating reactor in excess of thetheoretical hydrogen consumption. During the hydrotreating step,triglyceride oils, fatty acids and derivatives thereof are almosttheoretically converted to n-paraffins without or almost without sidereactions. Additionally, propane is formed from the glycerol part of thetriglycerides, water and CO and/or CO₂ from carboxylic oxygen, H₂S fromorganic sulphur compounds and NH₃ from organic nitrogen compounds. Usingthe above described procedures in the hydrotreating step, thetemperature needed for reactions to start up is achieved in thebeginning of each catalyst bed, the temperature increase in the catalystbeds is limited, harmful and partially converted product intermediatescan be avoided and the catalyst life is extended considerably. Thetemperature at the end of the catalyst bed is controlled by net heat ofreactions and to the extent of the dilution agent used. The dilutionagent may be any hydrocarbon available, of biological origin ornon-biological origin. It can also be recycled product from the process.Fresh feed content from feed (total feed) is be less than 20 wt-%. Ifthe product recycle is used, product recycle/fresh feed ratio is 5-30:1,preferably 10-30:1, most preferably 12-25:1. After the hydrotreatmentstep, the product is subjected to an isomerization step.

Feedstock

The bio oil and/or fat used as the fresh feed in the process of thepresent invention originates from renewable sources, such as fats andoils from plants and/or animals and/or fish and compounds derived fromthem. The basic structural unit of a typical plant or vegetable oranimal oil/fat useful as the feedstock is a triglyceride, which is atriester of glycerol with three fatty acid molecules, having thestructure presented in the following formula I:

In formula I R₁, R₂ and R₃ are alkyl chains. Fatty acids found innatural triglycerides are almost solely fatty acids of even carbonnumber. Therefore R₁, R₂, and R₃ typically are C₅-C₂₃ alkyl groups,mainly C₁₁-C₁₉ alkyl groups and most typically C₁₅ or C₁₇ alkyl groups.R₁, R₂, and R₃ may contain carbon-carbon double bonds. These alkylchains can be saturated, unsaturated or polyunsaturated.

Suitable bio oils are plant and vegetable oils and fats, animal fats,fish oils, and mixtures thereof containing fatty acids and/or fatty acidesters. Examples of suitable materials are wood-based and otherplant-based and vegetable-based fats and oils such as rapeseed oil,colza oil, canola oil, tall oil, sunflower oil, soybean oil, hempseedoil, olive oil, linseed oil, mustard oil, palm oil, peanut oil, castoroil, coconut oil, as well as fats contained in plants bred by means ofgene manipulation, animal-based fats such as lard, tallow, train oil,and fats contained in milk, as well as recycled fats of the foodindustry and mixtures of the above. Bio oil and fat suitable as freshfeed may comprise C₁₂-C₂₄ fatty acids, derivatives thereof such asanhydrides or esters of fatty acids as well as triglycerides of fattyacids or combinations of thereof. Fatty acids or fatty acid derivatives,such as esters may be produced via hydrolysis of bio oils or by theirfractionalization or transesterification reactions of triglycerides.

In order to avoid catalyst deactivation and undesired side reactions thefeed shall comply with the following requirements: The amount ofalkaline and alkaline earth metals, calculated as elemental alkaline andalkaline earth metals, in the feed is below 10, preferably below 5 andmost preferably below 1 w-ppm. The amount of other metals, calculated aselemental metals, in the feed is below 10, preferably below 5 and mostpreferably below 1 w-ppm. The amount of phosphorus, calculated aselemental phosphorus is below 30, preferably below 15 and mostpreferably below 5 w-ppm.

In many cases the feedstock, such as crude plant oil or animal fat, isnot suitable as such in processing because of high impurity content andthus the feedstock is preferably purified using suitably one or moreconventional purification procedures before introducing it to thehydrotreating step of the process. Examples of some conventionalprocedures are provided below:

Degumming of plant oils/fats and animal oils/fats means the removal ofphosphorus compounds, such as phospholipids. Solvent extracted vegetableoils often contain significant amounts of gums, typically 0.5-3% byweight, which are mostly phosphatides (phospholipids) and therefore adegumming stage is needed for crude plant oils and animal fats in orderto remove phospholipids and metals present in crude oils and fats. Ironand also other metals may be present in the form of metal-phosphatidecomplexes. Even a trace amount of iron is capable of catalysingoxidation of the oil or fat.

Degumming is performed by washing the feed at 90-105° C., 300−500kPa(a), with H₃PO₄, NaOH and soft water and separating the formed gums.A major amount of metal components, which are harmful for thehydrotreatment catalyst, are also removed from the feedstock during thedegumming stage. The moisture content of the degummed oil is reduced indryer at 90-105° C., 5-50 kPa(a).

A feedstock, which is optionally degummed or refined in anotherconventional way, may be bleached. In the bleaching the degummed orrefined feedstock is heated and mixed with natural or acid-activatedbleaching clay. Bleaching removes various impurity traces left fromother pretreatment steps like degumming, such as chlorophyll,carotenoids, phosphoipids, metals, soaps and oxidation products.Bleaching is typically carried out under vacuum to minimize possibleoxidation. Generally the goal of bleaching is to reduce the colorpigments in order to produce an oil of acceptable color and to reducethe oxidation tendency of oil.

Optionally the triglyceride structures of the feedstock may bedecomposed by prehydrogenating the double bonds using reduced reactiontemperature with NiMo or other catalyst, prior to the of byhydrodeoxygenations in order to prevent double bond polymerisation ofunsaturated triglycerides.

The process according to the invention is particularly advantageous whenthe fresh feed contains more than 5% of free fatty acids and even morethan 10% of free fatty acids. Thus also naturally occurring fats andoils containing significant amounts of free fatty acids can be processedwithout the removal of free fatty acids.

In the following the process according to the invention comprising ahydrotreating step and an isomerisation step is described in moredetail.

Hydrotreating of Bio Oils and Fats

In the first step of the process, i.e. in the hydrotreating step, fattyacids, triglycerides and other fatty acid derivatives comprised in thefeed are deoxygenated, denitrogenated and desulphurisated.

The feed comprises fresh feed and at least one dilution agent and theratio of the dilution agent/fresh feed is 5-30:1, preferably 10-30:1,most preferably 12-25:1.

The dilution agent is selected from hydrocarbons and recycled product ofthe process i.e. product recycle or mixtures thereof.

In the hydrotreating step, the pressure range may be varied between 20and 150 bar, preferably between 50 and 100 bar, and the temperaturebetween 200 and 400° C., preferably between 250 and 350° C. and mostpreferably between 280 and 340° C.

It was found that the selectivity of decarb-reactions and thedeoxygenation through decarb-reactions can be promoted duringhydrotreating over the hydrotreatment catalyst, by using sulphur contentof 50-20000 w-ppm, preferably 1000-8000 w-ppm, most preferably 2000-5000w-ppm of sulphur in the total feed, calculated as elemental sulphur. Thespecific sulphur content in the feed is able to double the extent ofn-paraffins formed by removal of COx. Complete deoxygenation oftriglycerides by decarb-reactions can theoretically lower theconsumption of hydrogen about 60% (max) compared with pure deoxygenationby hydrogen.

At least one organic or inorganic sulphur compound may optionally be fedalong with hydrogen or with the feed to achieve the desired sulphurcontent. The inorganic sulphur compound can be for example H₂S orelemental sulphur or the sulphur compound may be an easily decomposableorganic sulphur compound such as dimethyl disulphide, carbon disulfideand butyl thiol or a mixture of easily decomposable organic sulphurcompounds. It is also possible to use refinery gas or liquid streamscontaining decomposable sulphur compounds.

In the hydrotreatment/hydrodeoxygenation step, known hydrogenationcatalysts containing metals from Group VIII and/or VIB of the PeriodicSystem may be used. Preferably, the hydrogenation catalysts aresupported Pd, Pt, Ni, NiMo or a CoMo catalyst, the support being aluminaand/or silica, as described for instance in FI 100248. Typically,NiMo/Al₂O₃ and CoMo/Al₂O₃ catalysts are used.

In order to control the increase of temperature resulting from theaforementioned reactions over catalyst beds and side reaction formation,an improved reactor configuration is presented in FIG. 1. Thehydrotreatment section comprises one or more catalyst beds in series,dilution agent introduction on the top of the first catalyst bed andfresh feed, recycle liquid and hydrogen introduction on top of eachcatalyst beds. If the dilution agent is product recycle, the productrecycle/fresh oil-ratio is from 5-30:1, preferably 10-30:1 and mostpreferably 12-25:1. The catalyst beds can be located in same pressurevessel or each bed in a separate pressure vessel. Hydrogen is fed inexcess to the theoretical chemical hydrogen consumption and thefeedstock is converted totally or almost totally within each catalystbed. Using these procedures, harmful, partially converted productintermediates are avoided, the temperature needed for reactioninitiation is achieved in the beginning of each catalyst bed, the riseof reaction heating is controlled in the catalyst beds and the catalystlife is improved considerably.

Hydrodeoxygenation of triglycerides facilitates controlled decompositionof the triglyceride molecule contrary to uncontrolled cracking. Doublebonds are also hydrogenated during the controlled hydrotreatment. Lighthydrocarbons and gases formed, mainly propane, water, CO₂, CO, H₂S andNH₃ are removed from the hydrotreated product.

It was surprisingly observed in examples that product recycle dilutioncan prevent or remarkably decrease the reactions between free fattyacids and the formation of high molecular weight compounds duringhydrotreating, when at least 5:1 (product recycle):(fresh oil)-ratio wasused. The effect of product recycle is based on two phenomena: dilutioneffect of recycle and more controllable and reduced reactiontemperatures used over catalyst bed during hydrodeoxygenation. Highertemperatures and especially hot spots of catalyst bed promoteketonisation reactions. Due to this invention, it is possible to usevarious sources of bio oils and fats without the need to remove fattyacids. After the hydrotreatment step, the product is subjected to anisomerization step.

Isomerisation of N-Paraffins Formed During Hydrotreatment

In the second step of the process, i.e. in the isomerization step,isomerization is carried out which causes branching of the hydrocarbonchain and results in improved performance of the product oil at lowtemperatures. The isomerisation produces predominantly methyl branches.The severity of isomerisation conditions and choice of catalyst controlsthe amount of methyl branches formed and their distance from each otherand therefore cold properties of bio diesel fraction produced. Theproduct obtained from the hydrotreatment step is isomerised underisomerisation conditions with an isomerisation catalyst.

In the process according to the invention, the feed into theisomerisation reactor is a mixture of pure n-paraffins and thecomposition of it can be predicted from the fatty acid distribution ofindividual bio oils. During the hydrotreating step of the process,triglyceride oils and other fatty acid derivatives and fatty acids arealmost theoretically converted to n-paraffins. Additionally propane isformed from the glycerol part of triglycerides, water and COx fromcarboxylic oxygen, H₂S from organic sulphur compounds and NH₃ fromorganic nitrogen compounds. It is substantial for the process that thesegas phase impurities are removed as completely as possible before thehydrocarbons are contacted with the isomerization catalyst.

The isomerization step may comprise an optional stripping step, whereinthe reaction product from the hydrotreatment step may be purified bystripping with water vapour or a suitable gas such as light hydrocarbon,nitrogen or hydrogen. The optional stripping step is carried out incounter-current manner in a unit upstream of the isomerization catalyst,wherein the gas and liquid are contacted with each other, or before theactual isomerization reactor in a separate stripping unit utilizing thecounter-current principle.

In the isomerisation step, the pressure varies in the range of 20-150bar, preferably in the range of 30-100 bar and the temperature variesbetween 200 and 500° C., preferably between 280 and 400° C.

In the isomerisation step, isomerisation catalysts known in the art maybe used. Suitable isomerisation catalysts contain a molecular sieveand/or a metal selected from Group VIII of the Periodic Table and/or acarrier. Preferably, the isomerisation catalyst contains SAPO-11 orSAPO-41 or ZSM-22 or ZSM-23 or ferrierite and Pt, Pd or Ni and Al₂O₃ orSiO₂. Typical isomerization catalysts are, for example,Pt/SAPO-11/Al₂O₃, Pt/ZSM-22/Al₂O₃, Pt/ZSM-23/Al₂O₃ and Pt/SAPO-11/SiO₂.Most of these catalysts require the presence of hydrogen to reduce thecatalyst deactivation.

An isomerised product, which is a mixture of branched hydrocarbons andpreferably branched paraffins boiling in the range of 180-350° C., thediesel fuel range, and having one carbon atom less than the originalfatty acid chain, is obtained. Additionally some gasoline and gas may beobtained.

ADVANTAGES OF THE INVENTION

The invention provides a method for reducing the formation of highermolecular weight compounds during the hydrotreatment of a feed obtainedfrom plant oils and animal fats and which may contain free fatty acids.

It was surprisingly found that the problems of prior art processes maybe avoided or at least significantly reduced by the improved processaccording to the invention, comprising a hydrotreatment step and anisomerisation step wherein product recycle or another dilution agent inthe hydrotreatment step in combination with reduced operationtemperature result in important improvements, particularly when thefresh feed contains more than 5 wt % of free fatty acids. A specialreactor configuration and high dilution of fresh feed introduced intohydrotreatment are used in the method. The extent of side reactions isdecreased and the stability of catalyst during hydrotreating isincreased during the hydrotreatment step.

In the examples it was be seen that the ratio of at least 5:1(recycle:fresh) significantly decreased the formation of high molecularweight products, when the feedstock contains 10 wt-% of free fatty acids(calculated from fresh oil) is used. Using at least 5:1 recycle ratioand reduced reaction temperature, free fatty acids can be processedwithout the need for deacidification. High quality hydrocarbons areobtained, suitable for the diesel fuel pool with high yield.

The invention is illustrated in the following with examples presentingsome preferable embodiments of the invention. However, it is evident toa man skilled in the art that the scope of the invention is not meant tobe limited to these examples.

EXAMPLES

All hydrotreatment tests were performed in the presence of hydrogen.

Example 1 Comparative Example

Tall Oil Feed (100% Free Fatty Acids) without Product Recycle

Hydrotreating of tall oil (100% free fatty acids) with NiMo catalyst wascarried out at 50 bars pressure, LHSV 1.5 and reaction temperatures from340-360° C. without product recycle. Hydrogen oil ratio was 900 normalliters H₂ per liter oil fed. The hydrotreating of tall oil 100% freefatty acid feed caused rapid deactivation of NiMo catalyst, andformation of heavy weight compounds and aromatics was observed. Bromineindexes increased during the run even if temperature compensation ofcatalyst was used (FIG. 8). Product oil contained about 7 wt-% aromaticsand about 7 wt-% heavies (>375° C. boiling). Density (50° C.) of productoil was high 777.1 kg/m3 compared to typical values with rapeseed oilhydrotreated product oil (761-762 kg/m3) using lower reactiontemperature and optimized reaction conditions.

Example 2 Comparative Example

Tall Oil Fatty Acid Feed (100% FFA) at High Reaction Temperatureswithout Product Recycle

Hydrotreating of tall oil fatty acid feed (100% FFA) at high reactiontemperatures 370-385° C. was carried out without product recycle. Rapiddeactivation of NiMo catalyst and formation of heavy weight compoundsand aromatics was observed. Density of hydrotreated oil (table 1) wassignificantly higher than in rapeseed oil runs (typically 761-762kg/m3). Both oils contained mainly C18 fatty acids (˜90-wt-%) and rathersteady formation of water was observed during run. During the tall oilhydrotreating about 7-8 wt-% heavier molecular weight compounds and 8.1wt-% aromatics were formed. These side reactions are caused byconcentrated fatty acid feed and too high reaction temperatures.Deactivation of catalyst is clearly seen from increasing bromineindexes. During the satisfactory operation bromine index should be below50. Table 1 describes densities, bromine indexes, reaction temperaturesand water formed during test runs for 2 to 14 days using tall oil fattyacid feed (100% FFA) without recycling.

TABLE 1 Duration of test run 2nd 4th 6th 9th 11th 12th 13th 14th day dayday day day day day day Tempera- 370 375 378 381 385 385 385 385 ture, °C. Density, 771.8 773.1 773.7 776.5 779.1 779.8 780.5 781.2 50° C.,kg/m3 Bromine 101 150 188 198 247 269 300 330 index Product 9.37 9.59.81 10.3 10.2 10.0 10.1 10.2 water, %

Example 3 Comparative Example Effect of Metal Impurities of Bio Oils onthe Catalyst Performance

Tube reactor hydrotreatment test runs were carried out using cruderapeseed oil, crude animal fat and purified rapeseed oil. Analysis ofthese feeds are shown in Table 2. Crude feeds contained significantamount of metals, organic phosphorus, sulphur and nitrogen compounds.Purified feeds contained only trace levels of these impurities

TABLE 2 Impurity levels of crude and purified plant oils and animal fatsPurified Crude Crude Rapeseed Animal Impurity Unit Rapeseed oil oil fatMetals (total) ppm 90 ~0 162 Org. nitrogen ppm 33 7.2 1125 Free Fattyacid, GPC Wt-% 0.8 0.7 10.8 Total Acid Number mg KOH/g 1.0 0.1 21.5Phosphorous ppm 110 <1 86 Sulphur (original) ppm 3 1 85

Test runs using crude, unpurified oils/fats showed that catalyst neededhigher temperatures to work properly, but gradually lost its activity(FIG. 5). Triglycerides and increased bromine number of product oil wasfound. High amount of metals were also detected on to the catalyst.Temperature profile of the catalyst bed showed that top of the catalystbed was deactivated and reaction section moved forward (FIG. 4), whenreactor heating was maintained steady. Metals adsorbed on to thecatalyst also promote side reactions like decarb-reactions.

First hydrotreatment test run was carried out using crude rapeseed oil.Purified rapeseed oil was used as a reference feed. Purified rapeseedoil achieved complete HDO conversion at 305° C. using WHSV=2. Cruderapeseed oil gave total HDO conversion not until reaction temperature330° C. was used with space velocity WHSV=1. It was however seen fromtemperature profiles over the catalyst bed that first part of catalystwas deactivated very quickly. In FIG. 4, reaction temperature profileover catalyst bed and performance of crude rapeseed oil are presented.

Second hydrotreatment test run was carried out using purified rapeseedoil and crude animal fat. Purified rapeseed oil was used as a referencefeed. Purified rapeseed oil with product recycle achieved complete HDOconversion at 305° C. using WHSV=1. Crude animal fat with productrecycle did not give complete HDO conversion at 305° C. using WHSV=1. Itwas seen from GPC analyses that product oil contained triglycerides andcatalyst also significantly deactivated during crude animal fat feed.Pumping problems was also observed during crude animal fat feeding.Performance of crude animal fat is presented in FIG. 5.

Example 4 Comparative Example

Effect of Free Fatty Acids (10 wt-% in Fresh Feed) on the Formation ofHigh Molecular Weight Hydrocarbons

Hydrotreatment was carried out using purified rapeseed oil as referencefeed without product recycle. A test run was carried out at 305° C. and50 bars pressure using WHSV=1 and H₂/oil-ratio=1000. Sulphur content offeed was 570 ppm. During a second hydrotreatment test period stearicacid was fed (10 wt-% from rapeseed oil) along with purified rapeseedoil using same reaction conditions without product recycle. It was rightaway observed that the extent of high molecular weight compoundsincreased gradually from initial level ˜3 wt-% to ˜8 wt-%. These highermolecular weight compounds (molecular weight double or more of the feed)are not in the boiling range of diesel fuel and thus decrease dieselyield and potentially shorten the catalyst life. Thus free fatty acidsin bio oils make their processing more difficult. In FIG. 2 the increaseof formation of high molecular weight hydrocarbons is observed, when 10wt-% free fatty acids was fed along with purified rapeseed oiltriglycerides without product recycle.

Example 5

Effect of Product Recycle on Preventing Formation of Unwanted Heavy SideReaction Compounds when the Feed Contained 10 wt-% Free Fatty Acids

A hydrotreatment test run was carried out using 10 wt-% stearic acidcontaining purified rapeseed oil as reference feed without productrecycle under following reaction conditions: WHSV=1, 50 bars, 305° C.,H2/oil-ratio=1000 and sulphur content of feed=570 ppm. During the secondhydrotreatment test run period same feed was diluted with producthydrocarbons so that (fresh oil)/(product recycle)-ratio was 1:5. WHSVof fresh oil was maintained at 1, therefore WHSV of total oil feedincreased to 6. The reaction temperature was kept at 305° C. andreaction pressure at 50 bars. H₂/(fresh oil)-ratio was maintained at1000. HDO product (n-paraffins) simulated product recycle, which wasmixed in advance with fresh oil. The initial content of heavyhydrocarbons in the recycle was ˜0.4 wt-%.

It was unexpectedly observed that the formation of heavy hydrocarbonswas almost totally prevented or at least very significantly decreasedwhen product recycle was used (FIG. 3). This is most probably caused bysignificantly diminished side reactions of free fatty acids wherein acarboxylic acid molecule can react with another carboxylic acid moleculeto form a higher molecular weight compounds. In FIG. 3 the effect ofproduct recycle on preventing the formation of unwanted higher molecularweight by-product is presented. Table 3 presents analysis results of thefeed and products.

TABLE 3 Analysis results of the feed and products Feed analyses Productanalyses AR AR + 10 AR + 10 AR + 10 (10% SA) + wt-% stearic wt-% SA +wt-% SA + Recycle AR REC acid without Recycle after Recycle afterProperty Method Units AR feed (10% SA) 1:5 recycle 196 hours 552 hoursDensity, 15° C. D 4052 kg/m³ 920.4 788.1 915.8 807.2 790.8 788.3 788.3calc. Density, 50° C. D 4053 kg/m³ 897.6 761.4 893.2 781.2 764.2 761.7761.7 Br-index D 2710 mg/100 g 53.7 21.5 26 Br number D 1159 g/100 g 5649.1 6.3 Iodinenumber D 5554 g/100 g 112 103 18 HC GPC area-% 99.6 83.094.3 99.6 99.6 Fatty acids GPC area-% 0.7 0 10.6 1.8 0 0 0 Heavy HC GPCarea-% 0 0.4 0.5 5.7 0.4 0.4 Diglycerides GPC area-% 2.3 0 2.4 0 0 0Triglycerides GPC area-% 97 0 87 14.7 0 0 0 SA = Stearic acid, AR =purified rapeseed oil, REC = product recycle, HC = hydrocarbons, heavyHC = high molecular weight hydrocarbons

Example 6 Comparative Example The Effect of Lower Reaction Temperatureon the Selectivity of N-Paraffins and Oil Yield

Studies were carried out with NiMo catalyst using rapeseed oil as feedand reaction temperatures 280-330° C. and 340-360° C., WHSV=1 andreactor pressure of 50 bars. Alkali raffinated rapeseed oiltriglycerides contained mainly C₁₈ fatty acids. C₁₈ fatty acidscontributed about 89 wt-% of all fatty acids in rapeseed oil.Theoretical amount of n-paraffins formed from rapeseed oil fed is about86.4 wt-% (calculated from rapeseed oil fed).

Complete HDO conversion with almost theoretical n-paraffin yield wasaccomplished, when well controlled reaction temperatures <330° C. wereused. Almost theoretical n-paraffin yields tell us from complete HDOconversion and very controllable operation without significant sidereactions. High amount of side reactions (cyclisation, aromatisation andcracking) and low n-paraffin yield were observed when unnecessary highreaction temperatures 340-360° C. was used. In FIG. 6 the conversion ofrapeseed oil triglycerides to n-paraffins is presented.

Example 7 Stability of Catalyst

The stability of NiMo-catalyst using palm oil model feed (impuritiesadded) along with product recycle (catalyst life test) was carried outusing following reaction conditions: Reaction temperature=300-305° C.,Reactor pressure=40 bars, WHSV (fresh)=0.5, WHSV (total)=3, H₂/Oil(fresh)=900, Sulphur in feed=100 w-ppm. Palm oil was used as a maincomponent of feed, but it was modified with animal fat, fractions offree fatty acids, crude rapeseed oil, and lecithin in order to getsuitable specification of impurities of test feed. Fresh feed analysisis presented below in table 4. Fresh oil was then diluted in advancewith 1:5 ratio of HDO product (simulates product recycle). The durationof test run was over 9 months. Stabile operation was maintained (table 4and FIG. 7) and the formation of heavies was steady over the whole testrun FIG. 7.

TABLE 4 Stability of catalyst Product oil analysis Run duration FreshFeed 383 1898 3408 5601 Analysis Method Unit analysis hours hours hourshours Density, 15° C. D 4052 kg/m³ 804.9 787.4 785.6 785.3 784.9Density, 50° C. D 4052 kg/m³ 778.8 760.7 758.9 758.6 758.1 Br-index D2710 mg/100 g 29200 33 48 33 11 HC GPC area-% 0 99.3 99.4 99.3 99.4Fatty acids GPC area-% 1.2 0 0 0 0 Monoglyc/high GPC area-% 0.3 0.7 0.60.7 0.6 molec. weight HC Diglycerides GPC area-% 6.3 0 0 0 0Triglycerides GPC area-% 92.1 0 0 0 0 TAN D664 mg KOH/g 2.1 ~0 ~0 ~0 ~0Sulphur D 5453 ppm 3 1.2 2.0 2.7 2 Nitrogen D4629 mg/kg 6 <1 <1 1.2 <1Sodium, oil AAS mg/kg 3 0.4 <0.1 <0.1 <0.1 Calcium, oil AAS mg/kg 2 0.3<0.1 <0.1 <0.1 Magnesium, oil AAS mg/kg 0.3 <0.1 <0.1 <0.1 <0.1Molybdenum, oil AAS mg/kg — <0.5 <0.5 <0.5 <0.5 Aluminum, oil ICP metalsmg/kg <2 <2 <2 <2 <2 Iron, oil ICP metals mg/kg <1 <1 <1 <1 <1 Nickel,oil ICP metals mg/kg <1 <1 <1 <1 <1 Phosphorus, oil ICP metals mg/kg 4<1 <1 <1 <1

1. A process for the manufacture of diesel range hydrocarbons comprisingthe following steps: introducing a feedstock comprising bio oil and/orfat from renewable sources to a hydrotreatment step in whichhydrocarbons arc formed, isomerizing the formed hydrocarbons in anisomerization step, wherein gas phase impurities formed in thehydrotreatment step are removed from the stream comprising hydrocarbonsprior to contacting the hydrocarbons with the isomerization catalyst. 2.The process according to claim 1, further comprising a step of purifyingthe feedstock prior to the hydrotreatment step so as to removeimpurities.
 3. The process according to claim 1, wherein the gas phaseimpurities formed in the hydrotreatment step comprise propane, water,CO_(x), H₂S, NH₃ or mixtures thereof.
 4. The process according to claim1, wherein the removal of the gas phase impurities formed in thehydrotreatment step is performed in a stripping step upstream of theisomerization catalyst.
 5. The process according to claim 4, wherein thestripping step is performed by stripping with water vapor or a suitablegas comprising light hydrocarbon, nitrogen or hydrogen.
 6. The processaccording to claim 4, wherein the stripping step is carried out in acounter-current manner.
 7. The process according to claim 1, wherein thefeedstock comprises more than 10 wt % of free fatty acids.
 8. Theprocess according to claim 1, wherein the feedstock contains less than10 w-ppm alkaline and alkaline earth metals, calculated as elementalalkaline and alkaline earth metals, less than 10 w-ppm other metals,calculated as elemental metals, and less than 30 w-ppm phosphorus,calculated as elemental phosphorus.
 9. The process according to claim 2,wherein the purified feedstock contains less than 10 w-ppm alkaline andalkaline earth metals, calculated as elemental alkaline and alkalineearth metals, less than 10 w-ppm other metals, calculated as elementalmetals, and less than 30 w-ppm phosphorus, calculated as elementalphosphorus.
 10. The process according to claim 1, wherein the feedstockcontains 50-20000 w-ppm of sulphur, calculated as elemental sulphur. 11.The process according to claim 1, wherein the feedstock is selected fromplant oils/fats, animal fats/oils, fish fats/oils, fats contained inplants bred by means of gene manipulation, recycled fats of the foodindustry and mixtures thereof.
 12. The process according to claim 1,wherein the feedstock is selected from rapeseed oil, colza oil, canolaoil, tall oil, sunflower oil, soybean oil, hempseed oil, olive oil,linseed oil, mustard oil, palm oil, peanut oil, castor oil, coconut oil,lard, tallow, train oil or fats contained in milk.
 13. The processaccording to claim 1, wherein an isomerization catalyst containingmolecular sieve is used in the isomerization step.
 14. The processaccording to claim 2, wherein the gas phase impurities formed in thehydrotreatment step comprise propane, water, CO_(x), H₂S, NH₃ ormixtures thereof.
 15. The process according to claim 2, wherein theremoval of the gas phase impurities formed in the hydrotreatment step isperformed in a stripping step upstream of the isomerization catalyst.16. The process according to claim 2, wherein the stripping step isperformed by stripping with water vapor or a suitable gas comprisinglight hydrocarbon, nitrogen or hydrogen.
 17. The process according toclaim 2, wherein the stripping step is carried out in a counter-currentmanner.
 18. The process according to claim 2, wherein the purifiedfeedstock comprises more than 10 wt % of free fatty acids.
 19. Theprocess according to claim 2, wherein the purified feedstock contains50-20000 w-ppm of sulphur, calculated as elemental sulphur.
 20. Theprocess according to claim 2, wherein an isomerization catalystcontaining molecular sieve is used in the isomerization step.